Carrier-free semiconductor package

ABSTRACT

A carrier-free semiconductor package includes a circuit structure having an insulating layer and a circuit layer embedded in the insulating layer and having a plurality of conductive traces and RF (radio frequency) traces, a chip disposed on a first surface of the insulating layer and electrically connected to the conductive traces, an encapsulant covering the chip and the circuit layer, a ground layer formed on a second surface of the insulating layer opposite to the first surface, and a plurality of solder balls disposed on the conductive traces or terminals on the conductive traces, wherein portions of the solder balls electrically connect the ground layer so as to allow the RF traces and the ground layer to form a microstrip line having an RF function, thus obtaining a single-layer carrier-free semiconductor package having low cost and simplified RF design.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims under 35 U.S.C. §119(a) the benefit of TaiwaneseApplication No. 100108040, filed Mar. 10, 2011, the entire contents ofwhich is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to semiconductor packages and fabricationmethods thereof, and more particularly, to a carrier-free semiconductorpackage and a fabrication method thereof.

2. Description of Related Art

To meet consumer demands for convenience and portability, electronicproducts are becoming much lighter, thinner, shorter and smaller. Inaddition, electronic products are required to have high efficientperformance, low power consumption and multi-function. Generally,semiconductor chips are mounted on packaging substrates and encapsulatedso as to achieve high electrical performance However, the packagingsubstrates increase the overall thickness of final packages.

Accordingly, US Patent Application Publication No. 20080145967 disclosesa carrier-free semiconductor package and a fabrication method thereof,as shown in FIGS. 1A to 1H.

Referring to FIG. 1A, a carrier 10 is provided.

Referring to FIG. 1B, a resist layer 11 is formed on the carrier 10 anda plurality of openings 110 are formed in the resist layer 11 forexposing portions of the carrier 10.

Referring to FIG. 1C, by using the carrier 10 as a current conductivepath for electroplating, conductive traces 12 are formed on the portionsof the carrier 10 in the openings 110 of the resist layer 11.

Referring to FIG. 1D, the resist layer 11 is removed to expose thecarrier 10 and the conductive traces 12 on the carrier 10.

Referring to FIG. 1E, a mold 13 is disposed on the carrier 10. The mold13 has a mold cavity 130, and a plurality of protrusions 131 that abutagainst the conductive traces 12, respectively.

Referring to FIG. 1F, an insulating material is injected into the moldcavity 130 so as to form an insulating layer 14 in the mold cavity 130.Meanwhile, a plurality of openings 140 are formed at positionscorresponding to the protrusions 131.

Referring to FIG. 1G, the mold 13 and the carrier 10 are removed suchthat the conductive traces 12 are embedded in the insulating layer 14.Bottom surfaces of the conductive traces 12 are exposed through a bottomsurface of the insulating layer 14 while top surfaces of the conductivetraces 12 are exposed through the openings 140, respectively.

Referring to FIG. 1H, a plurality of solder balls 15 are disposed on thetop surfaces of the conductive traces 12 in the openings 140, and a chip16 is electrically connected to the bottom surfaces of the conductivetraces 12 exposed through the bottom surface of the insulating layer 14,thus forming a carrier-free semiconductor package.

However, the above-described single-layer carrier-free package isdifficult to be applied in RF (radio frequency) field, since a grounddesign is required for the characteristic impedance of a microstrip lineand also a carrier such as a dielectric layer needs to be disposedbetween RF traces and the ground.

Therefore, there is a need to provide a carrier-free semiconductorpackage having an RF function and a fabrication method thereof.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a carrier-free semiconductorpackage, which comprises: a circuit structure having an insulating layerwith opposite first and second surfaces, a circuit layer embedded in theinsulating layer and exposed from the first surface of the insulatinglayer and having a plurality of conductive traces and RF (radiofrequency) traces, and a plurality of openings formed on the secondsurface of the insulating layer for exposing the conductive traces,respectively; a chip disposed on the first surface of the insulatinglayer and electrically connected to the circuit layer; an encapsulantformed on the first surface of the insulating layer to cover the circuitlayer and the chip; and a ground layer formed on the second surface ofthe insulating layer and having a plurality of openings for exposing theopenings of the insulating layer and portions of the second surface ofthe insulating layer.

The above-described semiconductor package can further comprise aplurality of solder balls disposed on the conductive traces in theopenings of the insulating layer, wherein portions of the solder ballselectrically connect the ground layer. The circuit structure can furthercomprise a plurality of terminals formed on the conductive traces in theopenings of the insulating layer, and the solder balls are disposed onthe terminals, respectively.

The semiconductor package can further comprise a protection layer formedon the ground layer and the second surface of the insulating layer andhaving a plurality of openings for exposing the openings of theinsulating layer, respectively. Further, top surfaces of the terminalscan be flush with the second surface of the insulating layer.

The protection layer can be made of solder mask or polyimide.

The present invention further provides a fabrication method of acarrier-free semiconductor package, which comprises the steps of:forming on a carrier a circuit layer having a plurality of conductivetraces and RF traces; forming an insulating layer on the carrier and thecircuit layer, wherein the insulating layer has a plurality of openingsfor exposing the conductive traces, respectively, and has a firstsurface in contact with the carrier and a second surface opposite to thefirst surface; removing the carrier to expose the first surface of theinsulating layer and the circuit layer; disposing a chip on the firstsurface of the insulating layer and electrically connecting the chip andthe circuit layer; forming an encapsulant on the first surface of theinsulating layer to cover the circuit layer and the chip; and forming aground layer on the second surface of the insulating layer.

The method can further comprise the step of disposing a plurality ofsolder balls on the conductive traces in the openings of the insulatinglayer, respectively, wherein portions of the solder balls electricallyconnect the ground layer.

Before removing the carrier, the method can further comprise the step offorming terminals on the conductive traces in the openings of theinsulating layer such that the solder balls can be disposed on theterminals.

The step of forming the circuit layer can comprise the steps of: formingon the carrier a first resist layer having a plurality of openings forexposing portions of the carrier; forming the circuit layer on theportions of the carrier in the openings of the first resist layer; andremoving the first resist layer to expose the carrier and the circuitlayer on the carrier.

The step of forming the insulating layer and the openings of theinsulating layer can comprise the steps of: disposing on the carrier amold having a mold cavity and a plurality of protrusions, wherein theprotrusions abut against the conductive traces of the circuit layer,respectively; injecting an insulating material into the mold cavity soas to form the insulating layer; and removing the mold to expose theinsulating layer, thereby forming the openings of the insulating layercorresponding in position to the protrusions of the mold for exposingthe conductive traces, respectively.

The step of forming the ground layer can comprise the steps of: forminga metal layer on the second surface of the insulating layer; andpatterning the metal layer to form the ground layer having a pluralityof openings for exposing the openings of the insulating layer andportions of the second surface of the insulating layer.

After forming the ground layer, the method can further comprise the stepof forming a protection layer on the ground layer and the second surfaceof the insulating layer, wherein the protection layer has a plurality ofopenings for exposing the openings of the insulating layer,respectively.

The present invention provides another fabrication method of acarrier-free semiconductor package. Different from the above-describedmethod, the present method comprises the step of forming terminals onthe conductive traces, respectively, before forming the insulatinglayer.

Further, the step of forming the circuit layer and the terminals cancomprise the steps of: forming on the carrier a first resist layerhaving a plurality of openings for exposing portions of the carrier;forming the circuit layer on the portions of the carrier in the openingsof the first resist layer; removing the first resist layer to expose thecarrier and the circuit layer on the carrier; forming a second resistlayer on the carrier and the circuit layer, the second resist layerhaving a plurality of openings for exposing the conductive traces of thecircuit layer, respectively; forming the terminals on the conductivetraces in the openings of the second resist layer; and removing thesecond resist layer.

Therefore, the present invention involves forming a circuit structurehaving an insulating layer and a circuit layer embedded in theinsulating layer and having a plurality of conductive traces and RFtraces, disposing a chip on a first surface of the insulating layer andelectrically connecting the chip and the conductive traces, forming anencapsulant to cover the chip and the circuit layer, forming a groundlayer on a second surface of the insulating layer opposite to the firstsurface, and disposing a plurality of solder balls on the conductivetraces or terminals on the conductive traces, wherein portions of thesolder balls electrically connect the ground layer so as to allow the RFtraces and the ground layer to form a microstrip line having an RFfunction, thus obtaining a single-layer carrier-free semiconductorpackage having low cost and simplified RF design.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A to 1H are schematic cross-sectional views showing asemiconductor package and a fabrication method thereof according to USPatent Application Publication No. 2008/0145967;

FIGS. 2A to 2M are schematic cross-sectional views showing acarrier-free semiconductor package and a fabrication method thereofaccording to a first embodiment of the present invention, wherein FIG.2G′ shows another embodiment of FIG. 2G and FIG. 2M′ shows anotherembodiment of FIG. 2M; and

FIGS. 3A to 3I are schematic cross-sectional views showing acarrier-free semiconductor package and a fabrication method thereofaccording to a second embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following illustrative embodiments are provided to illustrate thedisclosure of the present invention, these and other advantages andeffects can be apparent to those in the art after reading thisspecification.

It should be noted that all the drawings are not intended to limit thepresent invention. Various modification and variations can be madewithout departing from the spirit of the present invention. Further,terms such as “one”, “above”, etc. are merely for illustrative purposeand should not be construed to limit the scope of the present invention.

First Embodiment

FIGS. 2A to 2M are cross-sectional views showing a carrier-freesemiconductor package and a fabrication method thereof according to afirst embodiment of the present invention.

Referring to FIG. 2A, a carrier 20 made of metal is provided. A firstresist layer 21 a is formed on the carrier 20 and patterned so as toform a plurality of openings 210 a in the first resist layer 21 a forexposing portions of the carrier 20.

Referring to FIG. 2B, an electroplating process is performed to form acircuit layer 22 on the portions of the carrier 20 in the openings 210 aof the first resist layer 21 a. Therein, the circuit layer 22 comprisesa plurality of conductive traces 221 and RF traces 222.

Referring to FIG. 2C, the first resist layer 21 a is removed to exposethe carrier 20 and the circuit layer 22 on the carrier 20.

Referring to FIG. 2D, a mold 23 having a mold cavity 230 and a pluralityof protrusions 231 is disposed on the carrier 20, and the protrusions231 abut against the conductive traces 221 of the circuit layer 22,respectively.

Referring to FIG. 2E, an insulating material is injected into the moldcavity 230 of the mold 23 so as to form an insulating layer 24 in themold cavity 230. After the insulating material is cured, the mold 23 isremoved, thereby forming on the carrier 20 the insulating layer 24having a plurality of openings 240 corresponding in position to theprotrusions 231 of the mold for exposing the conductive traces 221,respectively. The insulating layer 24 has a first surface 24 a incontact with the carrier 20 and a second surface 24 b opposite to thefirst surface 24 a.

Referring to FIG. 2F, a plurality of terminals 25 are formed on theconductive traces 221 in the openings 240 by electroplating. In anotherembodiment, no terminals 25 are formed, and a plurality of solder balls30 are directly disposed on the conductive traces 221 in the openings240. In addition, an OSP (organic solderability preservative) processcan be performed to the terminals 25.

Referring to FIG. 2G, the carrier 20 is removed such that the firstsurface 24 a of the insulating layer 24 and the circuit layer 22 areexposed to form a circuit structure 2. Alternatively, referring to FIG.2G′, a copper layer 31 is formed on the terminals 25 and the secondsurface 24 b of the insulating layer 24. Then, the carrier 20 isremoved, and an electroplating process is performed to form on theconductive traces 221 a bondable metal layer 32 made of such asNi/Pd/Au. Subsequently, the copper layer 31 is removed.

Referring to FIG. 2H, the circuit structure 2 is turned upside down suchthat the first surface 24 a of the insulating layer 24 faces up.Further, a chip 26 having a plurality of electrode pads 261 is disposedon the first surface 24 a of the insulating layer 24 and a plurality ofbonding wires 262 are formed to electrically connect the conductivetraces 221 on the first surface 24 a and the electrode pads 261 of thechip 26. Alternatively, the chip 26 can be flip-chip electricallyconnected to the circuit layer 22.

Referring to FIG. 2I, an encapsulant 27 is formed on the first surface24 a of the insulating layer 24 to cover the circuit layer 22, the chip26 and the bonding wires 262.

Referring to FIG. 2J, a metal layer 28 is formed on the second surface24 b of the insulating layer 24, in the openings 240 and on theterminals 25 through physical vapor deposition (PVD) or chemical vapordeposition (CVD).

Referring to FIG. 2K, the metal layer 28 is patterned so as to form aground layer 28′ on the second surface 24 b and form a plurality ofopenings 280 in the metal layer 28 for exposing the terminals 25, theopenings 240 and portions of the second surface 24 b of the insulatinglayer 24.

Referring to FIG. 2L, a protection layer 29 made of solder mask orpolyimide is formed on the ground layer 28′ and the second surface 24 bof the insulating layer 24, and a plurality of openings 290 are formedin the protection layer 29 by exposure and development or laser drillingso as to expose the openings 240 of the insulating layer 24, theterminals 25 and portions of side surfaces 28 a of the ground layer 28′.

Referring to FIG. 2M, a plurality of solder balls 30 are disposed on theterminals 25 in the openings 290 of the protection layer 29, andportions of the solder balls 30 electrically connect the ground layer28′ so as to allow the RF traces 222 and the ground layer 28′ to form amicrostrip line having an RF function.

In another embodiment, referring to FIG. 2M′, no terminals 25 are formedand a plurality of solder balls 30 are directly disposed on theconductive traces 221 in the openings 240 of the insulating layer 24.

Second Embodiment

FIGS. 3A to 3I show a fabrication method of a carrier-free semiconductorpackage according to a second embodiment of the present invention.

Referring to FIG. 3A, a carrier 20 is provided. A first resist layer 21a is formed on the carrier 20 and then patterned so as to form aplurality of openings 210 a in the first resist layer 21 a for exposingportions of the carrier 20.

Referring to FIG. 3B, the carrier 20 is used as a current conductivepath for electroplating so as to form a circuit layer 22 on the portionsof the carrier 20 in the openings 210 a. Therein, the circuit layer 22comprises a plurality of conductive traces 221 and a plurality of RFtraces 222.

Referring to FIG. 3C, the first resist layer 21 a is removed to exposethe carrier 20 and the circuit layer 22 on the carrier 20.

Referring to FIG. 3D, a second resist layer 21 b is formed on thecarrier 20 and the circuit layer 22 and then patterned so as to form aplurality of openings 210 b in the second resist layer 21 b for exposingthe conductive traces 221 of the circuit layer 22.

Referring to FIG. 3E, by using the carrier 20 as a current conductivepath for electroplating, a plurality of terminals 25′ are formed on theconductive traces 221 in the openings 210 b by electroplating.

Referring to FIG. 3F, the second resist layer 21 b is removed to exposethe carrier 20, the circuit layer 22 and the terminals 25′.

Referring to FIG. 3G, an insulating layer 24 is formed on the carrier20, the circuit layer 22 and the terminals 25′. The insulating layer 24has a first surface 24 a in contact with the carrier 20 and a secondsurface 24 b opposite to the first surface 24 a, and top surfaces of theterminals 25′ are exposed from the second surface 24 b of the insulatinglayer 24. In the present embodiment, the top surfaces of the terminals25′ are flush with the second surface 24 b of the insulating layer 24.

Referring to FIG. 3H, the carrier 20 is removed such that the firstsurface 24 a of the insulating layer 24 and the circuit layer 22 areexposed to form a circuit structure 2.

Referring to FIG. 3I, the processes as described in FIGS. 2H to 2M ofthe first embodiment are performed to dispose a chip 26 on the circuitstructure 2, form a plurality of bonding wires 262 electricallyconnecting the chip 26 and the circuit structure 2, form an encapsulant27 to cover the circuit layer 22, the chip 26 and the bonding wires 262,form a ground layer 28′ on the insulating layer 24 of the circuitstructure 2, form a protection layer 29 on the ground layer 28′ and theinsulating layer 24, and dispose a plurality of solder balls 30 on theconductive traces 221. Therein, the ground layer 28′ is electricallyconnected to the ground of an external circuit board through portions ofthe solder balls 30 to thereby form a microstrip line in combinationwith the RF traces 222.

According to the above-described processes, the present inventionfurther provides a carrier-free semiconductor package, which has acircuit structure 2, a chip 26, an encapsulant 27, a ground layer 28′and a plurality of solder balls 30 disposed on the circuit structure 2.

Therein, the circuit structure 2 has an insulating layer 24 withopposite first and second surfaces 24 a, 24 b, a circuit layer 22embedded in the insulating layer 24 and expose from the first surface 24a of the insulating layer 24 and having a plurality of conductive traces221 and RF traces 222, a plurality of openings 240 formed on the secondsurface 24 b of the insulating layer 24 for exposing the conductivetraces 221, respectively, and a plurality of terminals 25 formed on theconductive traces 221 in the openings 240.

The chip 26 is disposed on the first surface 24 a of the insulatinglayer 24 and having a plurality of electrode pads 261 electricallyconnected to the circuit layer 22 through bonding wires or in aflip-chip manner.

The encapsulant 27 is formed on the first surface 24 a of the insulatinglayer 24 to cover the circuit layer 22, the chip 26 and the bondingwires 262.

The ground layer 28′ is formed on the second surface 24 b of theinsulating layer 24 and has a plurality of openings 280 for exposing theterminals 25 and portions of the second surface 24 b of the insulatinglayer 24.

The solder balls 30 are disposed on the terminals 25 and portions of thesolder balls 30 electrically connect the ground layer 28′.

The carrier-free package can further comprise a protection layer 29formed on the ground layer 28′ and the second surface 24 b of theinsulating layer 24. Further, the protection layer 29 has a plurality ofopenings 290 for exposing the openings 240 of the insulating layer 24,the terminals 25, and portions of side surfaces 28 a of the ground layer28′. The protection layer 29 can be made of solder mask or polyimide.

As described above, the top surfaces of the terminals 25′ can be flushwith the second surface 24 b of the insulating layer 24.

Therefore, the present invention involves forming a circuit structurehaving an insulating layer and a circuit layer embedded in theinsulating layer and having a plurality of conductive traces and RFtraces, disposing a chip on a first surface of the insulating layer andelectrically connecting the chip and the conductive traces, forming anencapsulant to cover the chip and the circuit layer, forming a groundlayer on a second surface of the insulating layer opposite to the firstsurface, forming a protection layer on the ground layer and the secondsurface of the insulating layer and forming a plurality of openings inthe protection layer for exposing the conductive traces or terminals onthe conductive traces and portions of sides surfaces of the groundlayer, and disposing a plurality of solder balls on the conductivetraces or the terminals in the openings of the protection layer, whereinportions of the solder balls electrically connect the exposed sidesurfaces of the ground layer so as to allow the RF traces and the groundlayer to form a microstrip line having an RF function, thus obtaining asingle-layer carrier-free semiconductor package having low cost andsimplified RF design.

The above-described descriptions of the detailed embodiments are only toillustrate the preferred implementation according to the presentinvention, and it is not to limit the scope of the present invention.Accordingly, all modifications and variations completed by those withordinary skill in the art should fall within the scope of presentinvention defined by the appended claims.

What is claimed is:
 1. A semiconductor package, comprising: a circuitstructure having an insulating layer with opposite first and secondsurfaces, a circuit layer embedded in the insulating layer and exposedfrom the first surface of the insulating layer and having a plurality ofconductive traces embedded in the insulating layer and radio frequency(RF) traces embedded in the insulating layer, and a plurality ofopenings formed on the second surface of the insulating layer forexposing the conductive traces, respectively; a chip disposed on thefirst surface of the insulating layer and electrically connected to theconductive traces of the circuit layer, wherein the chip is free frombeing electrically connected to the radio frequency (RF) traces of thecircuit layer; an encapsulant formed on the first surface of theinsulating layer to cover the circuit layer and the chip; and a groundlayer formed on the second surface of the insulating layer and having aplurality of openings for exposing the openings of the insulating layerand portions of the second surface of the insulating layer.
 2. Thesemiconductor package of claim 1, further comprising a plurality ofsolder balls disposed on the conductive traces in the openings of theinsulating layer, wherein portions of the solder balls electricallyconnect the ground layer.
 3. The semiconductor package of claim 1,wherein the circuit structure further comprises a plurality of terminalsformed on the conductive traces in the openings of the insulating layer.4. The semiconductor package of claim 3, further comprising a pluralityof solder balls disposed on the terminals, respectively, whereinportions of the solder balls electrically connect the ground layer. 5.The semiconductor package of claim 3, wherein top surfaces of theterminals are flush with the second surface of the insulating layer. 6.The semiconductor package of claim 1, further comprising a protectionlayer formed on the ground layer and the second surface of theinsulating layer and having a plurality of openings for exposing theopenings of the insulating layer, respectively.
 7. The semiconductorpackage of claim 6, wherein the protection layer is made of solder maskor polyimide.